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Hey guys, new member here...puzzled with this truck, and though I've searched and read on this subject for hours, I'm hoping someone may be able to relate to this specific experience a little more.
Just purchased 05 Yukon XL Denali (6.0), 175k miles. Truck ran and drove excellent upon inspection, with one mechanical caveat; oil pressure gauge was pegged at 80lbs. I wasn't concerned, as I expected a sending unit to be a quick solution, engine runs very quiet, no valvetrain noise, and previous owner(11 years) seemed very honest and had maintained the vehicle well, though he was not a 'car guy'. He did tell me that the oil pump was replaced 1.5yrs ago, and had no issues since(though he didn't seem to have noticed the guage stuck at 80lbs, in hindsight ??)
Anyway, I drove the truck home 200 miles in 85 degree weather, AC on most of the way, no issues.
The next day, changed the oil and replaced the sending unit simultaneously (Mobil 1 5w30 and Mobil 1 filter, AutoZone sender). First start up, oil pressure gauge rose to just above 10, then fell to 5, low pressure warning on. Engine quiet as ever.
Here's where it gets weird...manual guage at sender port reflects dash guage. I was able to remove the plug in the engine block oil galley, manual guage shows 25+ at idle, 40-50psi under throttle.
I have since done the following:
Removed sender, threaded a port with a hose attached in it's place to confirm flow(in the unlikely case of blockage), oil is there.
Replaced pick up tube o ring, and cleaned and inspected, plus shop air through the pick up tube, and all oil pan ports, including cooler ports and lines in case of blockage. Inside of pan and bottom of engine were clean, zero sludge, virtually no shavings or anything out of the ordinary.
Replaced the cooler line fittings at the radiator, as they were leaking.
Switched to conventional 10w40 and AC Delco filter.
Ran engine with valve cover removed, definitely has the appearance of low pressure, very little oil entering the top of the engine, definitely not splattering like I would expect with cover off.

All of this to me points to an oil pump issue(replaced or not), except for the fact that I'm showing decent pressure at the oil galley port, and almost none at the sender. A very reputable local mechanic has told me he does not understand that either, as he would expect pressure to be nearly static, except in the case of a massive leak. He still said if I brought it to him, he would recommend going ahead and replacing the pump anyway, because it seems the next logical step. So I am prepared to swap the pump...but I have also seen tidbits of info about the oil galley barbell and plug possibly presenting this issue...though most of these cases seem to be where guys have forgotten to install the barbell in a new engine build.
Does anyone have any experience with these somehow breaking or coming out of an existing engine, and if so, does this create a 0 pressure or just low pressure situation? Is it even possible?
Or any other insight to lend before I just replace the pump as the next step along the way?

One other note, engine currently idles(per dash guage) around 5-7psi, keeping the warning light on, except for under initial startup (30-45 seconds, it stays near 15). During driving conditions, as long as you keep the rpms above 1500, it will hold at 20lbs on the guage, and keep the light off. Near 3000 rpms, it may get just a bit over 20, but minimal.

Apologies for the long winded post, I'm just not understanding this situation, and while obviously replacing the pump is not a major cost or extremely time consuming, I'm tired of working on it with 0 results. Appreciate any help you can provide!
 

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2001 Suburban 5.3L, 302.2k miles
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Check the oil pressure relief spring and plunger, oil could be bypasing there.
 

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Hey guys, new member here...puzzled with this truck, and though I've searched and read on this subject for hours, I'm hoping someone may be able to relate to this specific experience a little more.
Just purchased 05 Yukon XL Denali (6.0), 175k miles. Truck ran and drove excellent upon inspection, with one mechanical caveat; oil pressure gauge was pegged at 80lbs. I wasn't concerned, as I expected a sending unit to be a quick solution, engine runs very quiet, no valvetrain noise, and previous owner(11 years) seemed very honest and had maintained the vehicle well, though he was not a 'car guy'. He did tell me that the oil pump was replaced 1.5yrs ago, and had no issues since(though he didn't seem to have noticed the guage stuck at 80lbs, in hindsight ??)
Anyway, I drove the truck home 200 miles in 85 degree weather, AC on most of the way, no issues.
The next day, changed the oil and replaced the sending unit simultaneously (Mobil 1 5w30 and Mobil 1 filter, AutoZone sender). First start up, oil pressure gauge rose to just above 10, then fell to 5, low pressure warning on. Engine quiet as ever.
Here's where it gets weird...manual guage at sender port reflects dash guage. I was able to remove the plug in the engine block oil galley, manual guage shows 25+ at idle, 40-50psi under throttle.
I have since done the following:
Removed sender, threaded a port with a hose attached in it's place to confirm flow(in the unlikely case of blockage), oil is there.
Replaced pick up tube o ring, and cleaned and inspected, plus shop air through the pick up tube, and all oil pan ports, including cooler ports and lines in case of blockage. Inside of pan and bottom of engine were clean, zero sludge, virtually no shavings or anything out of the ordinary.
Replaced the cooler line fittings at the radiator, as they were leaking.
Switched to conventional 10w40 and AC Delco filter.
Ran engine with valve cover removed, definitely has the appearance of low pressure, very little oil entering the top of the engine, definitely not splattering like I would expect with cover off.

All of this to me points to an oil pump issue(replaced or not), except for the fact that I'm showing decent pressure at the oil galley port, and almost none at the sender. A very reputable local mechanic has told me he does not understand that either, as he would expect pressure to be nearly static, except in the case of a massive leak. He still said if I brought it to him, he would recommend going ahead and replacing the pump anyway, because it seems the next logical step. So I am prepared to swap the pump...but I have also seen tidbits of info about the oil galley barbell and plug possibly presenting this issue...though most of these cases seem to be where guys have forgotten to install the barbell in a new engine build.
Does anyone have any experience with these somehow breaking or coming out of an existing engine, and if so, does this create a 0 pressure or just low pressure situation? Is it even possible?
Or any other insight to lend before I just replace the pump as the next step along the way?

One other note, engine currently idles(per dash guage) around 5-7psi, keeping the warning light on, except for under initial startup (30-45 seconds, it stays near 15). During driving conditions, as long as you keep the rpms above 1500, it will hold at 20lbs on the guage, and keep the light off. Near 3000 rpms, it may get just a bit over 20, but minimal.

Apologies for the long winded post, I'm just not understanding this situation, and while obviously replacing the pump is not a major cost or extremely time consuming, I'm tired of working on it with 0 results. Appreciate any help you can provide!
Had the same problem with my 05 Denali. Read all sorts of fixes some very expensive. Decided to put some of the Sea Foam I had into the oil, about 6 ounces. Drive it for a couple hundred miles, changed the oil and like magic got 25 extra psi. Hope this helps.
 

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2000 Silverado Z71 4x4 5.3L 480k+ miles w/ GM rebuilt motor and trans
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Had the same problem with my 05 Denali. Read all sorts of fixes some very expensive. Decided to put some of the Sea Foam I had into the oil, about 6 ounces. Drive it for a couple hundred miles, changed the oil and like magic got 25 extra psi. Hope this helps.
Had success with this in a 2013 with the collapsed AFM lifter. Increased pressure, unstuck lifter, deactivated AFM.
 

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Discussion Starter · #6 ·
Had the same problem with my 05 Denali. Read all sorts of fixes some very expensive. Decided to put some of the Sea Foam I had into the oil, about 6 ounces. Drive it for a couple hundred miles, changed the oil and like magic got 25 extra psi. Hope this helps.
Thanks, I'll have to give this a shot!
 
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